An antenna (or aerial) is an electrical device that converts electric power into radio waves, and vice versa. An antenna can be used with a radio transmitter and/or radio receiver. In transmission, a radio transmitter supplies an oscillating radio frequency electric current to the antenna's terminals, and the antenna radiates the energy from the current as electromagnetic waves (radio waves). In reception, an antenna intercepts some of the power of an electromagnetic wave in order to produce a small voltage at the antenna's terminals that is applied to a receiver to be amplified. An antenna's radiation pattern (also referred to as an antenna pattern or far-field pattern) can refer to the directional (angular) dependence of the strength of the radio waves from the antenna.